1) Field of the Invention
The present invention relates to a bus power device based on an interface standard of universal serial bus (USB), Institute of Electrical and Electronics Engineers (IEEE) 1394, and the like. More particularly, the present invention relates to a bus power device and a power-source control method that can avoid an inoperative state due to a voltage drop or the like, figure out a battery remaining level according to an operation status, and charge the battery quickly.
2) Description of the Related Art
Recently, as an interface to connect a peripheral device to a personal computer, the USB interface standard attracts attention. The USB interface standard has a characteristic that the interface can connect maximum of 127 USB devices in a tree structure.
FIG. 7 is a block diagram of a configuration of a conventional bus power device 20. In this drawing, a USB-corresponding device 10 is a personal computer corresponding to the USB interface standard, and has a high-power USB port 11. A hub 13 has a low-power USB port 12 that is driven with bus power.
The high-power USB port 11 is connected with a USB connector (i.e., a USB connector 30 in the drawing) and can supply high power. The high-power USB port 11 has a basic function as a data input/output port, and a function of supplying rated power of 2.5 watts (500 mA/5 V) to the USB device (i.e., the bus power device 20 in the drawing).
The low-power USB port 12 is a low-power port connected with the USB connector, and has a function as a data input/output port, and a function of supplying rated power of 0.5 watt (100 mA/5 V) to the USB device. However, the USB device connected to the low-power USB port 12 is not driven with low power of 0.5 watt, but is a self-power unit that is driven with power received from a separate power source.
The bus power device 20 is a hard disk drive unit as one USB device, and is driven with high power (2.5 watts (500 mA/5 V)) supplied from the USB-corresponding device 10 via the USB connector 30 connected to the high-power USB port 11.
The USB connector 30 is based on the USB interface standard, and is connected to the high-power USB port 11 when the bus power device 20 is used. The USB connector 30 is also connected to a bus power line 31 to supply power to each section, a data line 32, a ground (GND) line, a shield line, and the like.
A USB/AT attachment (USB/ATA) converter 21 has a function of converting data of the USB interface standard input through a data line 32 into data of an ATA interface standard, and outputting the converted data to a hard disk 23 via an ATA interface 22.
The hard disk 23 is a large-capacity recording medium which is rotatably driven with power supplied through the bus power line 31 to read/write data.
The USB/ATA converter 21 has a function of converting the data of the ATA interface standard read from the hard disk 23 and input via the ATA interface 22, into data of the USB interface standard, and outputting the converted data to the data line 32.
A voltage adjustor 24 adjusts a voltage of 5 V supplied through the bus power line 31 into a voltage of 3.3 V, and supplies this voltage to the USB/ATA converter 21.
The operation by the bus power device 20 is explained with reference to a flowchart shown in FIG. 8. At step SA1 in the drawing, the USB connector 30 is connected to the high-power USB port 11, and is plugged in. At step SA2, the USB-corresponding device 10 acknowledges the bus power device 20.
At step SA3, it is determined whether the USB connector 30 is connected to the high-power USB port 11. In this case, the determination result is “Yes”. At step SA4, the USB-corresponding device 10 supplies the high power (500 mA/5 V) to the voltage adjustor 24 and the hard disk 23 through the bus power line 31.
As a result, at step SA5, the voltage adjustor 24 supplies the voltage of 3.3 V to the USB/ATA converter 21, so that the USB/ATA converter 21 starts operation and the hard disk 23 also starts operation.
On the other hand, when the determination result at step SA3 is “No”, that is, when the USB connector 30 is connected to the low-power USB port 12, the USB-corresponding device 10 supplies only the low power (100 mA/5 V) to each section of the bus power device 20. Therefore, at step SA6, the bus power device 20 is unusable.
According to the bus power device 20 shown in FIG. 7, depending on the operation condition, immediately after the USB connector 30 is connected to the USB-corresponding device 10, an inrush current flows through the bus power line 31 at the initial rotation of the hard disk 23. This has a problem in that the current supplied from the USB-corresponding device 10 to the bus power device 20 may exceed a predetermined value (500 mA), leading to a malfunction or an operation failure.
To solve this problem, the conventional bus power device employs a current assisting system by having a secondary battery. When the current that flows through the bus power line 31 exceeds a predetermined value, the secondary battery countervails an overcurrent, or assists to decrease the current that is supplied from the high-power USB port 11 to the bus power device 20.
FIG. 9 is a block diagram of a configuration of a conventional bus power device 40 according to the current assisting system. In the drawing, like reference numerals as those in FIG. 7 designate like parts, and their explanation is omitted.
In the bus power device 40 in the drawing, a secondary battery 41 is a lithium ion battery, an alkali battery, a nickel cadmium battery, or the like that can be repetitively charged and discharged. When the current flowing through the bus power line 31 exceeds a predetermined value, the secondary battery 41 supplies an overcurrent to each section through the bus power line 31.
A current detector 42 detects a current that flows through the bus power line 31. An micro processing unit (MPU) 43 has a function of controlling the current assist based on the result of the current detection by the current detector 42, a function of controlling a charge to the secondary battery 41, a function of controlling a power supply to the hard disk 23, a function of controlling a display of a battery remaining level, a function of monitoring a status of the USB/ATA converter 21, and the like.
A hard disk power source switch 44 is present between the bus power line 31 and the hard disk 23, and has a function of turning on/off a power supply to the hard disk 23 under the control of the MPU 43. A charger 45 is present between the bus power line 31 and the secondary battery 41, and has a function of charging a current flowing through the bus power line 31 to the secondary battery 41 under the control of the MPU 43.
A current assisting unit 46 is present between the secondary battery 41 and the bus power line 31, and has a current assisting function of supplying an overcurrent from the secondary battery 41 to the bus power line 31 under the control of the MPU 43 when a current exceeding a predetermined value flows to the bus power line 31.
A battery remaining level display unit 47 displays a battery remaining level of the secondary battery 41 by lighting/flickering a light emitting diode (LED) under the control of the MPU 43. Specifically, when the battery voltage of the secondary battery 41 exceeds a threshold value, the LED lights up to inform a user that the battery remaining level is sufficient. On the other hand, when the battery voltage of the secondary battery 41 becomes equal to or lower than the threshold value, the LED flickers to inform the user that there is only small room in the battery remaining level.
In the above configuration, when the USB connector 30 is connected to the high-power USB port 11 and is plugged in, the USB-corresponding device 10 acknowledges the bus power device 40.
As a result, the USB-corresponding device 10 supplies the high power (500 mA/5 V) to each section through the bus power line 31 to activate each section. Specifically, the voltage adjustor 24 supplies a voltage of 3.3 V to the USB/ATA converter 21, so that the USB/ATA converter 21 starts operation. When the hard disk power source switch 44 is turned on under the control of the MPU 43, the bus power line 31 supplies power to the hard disk 23, so that the hard disk 23 starts operation.
When an inrush current flows through the bus power line 31 due to the initial rotation of the hard disk 23 and when this current exceeds a predetermined value, a current assist is carried out. In other words, when the current detected by the current detector 42 exceeds the predetermined value, the MPU 43 instructs the current assisting unit 46 to assist the current.
As a result, the current assisting unit 46 discharges the secondary battery 41, and supplies the current from the secondary battery 41 to the bus power line 31. Accordingly, the current detector 42 detects that the current becomes equal to or smaller than the predetermined value, because the current is smaller by the current discharged from the secondary battery 41.
When the current detected by the current detector 42 is equal to or smaller than the predetermined value, the current assisting unit 46 does not need to assist the current, and therefore, the MPU 43 outputs a charge pulse to the charger 45.
Therefore, the charger 45 supplies a part of the current from the bus power line 31 to the secondary battery 41 to charge the secondary battery 41. The MPU 43 makes the battery remaining level display unit 47 display a battery remaining level of the secondary battery 41 based on a result of monitoring the battery voltage.
When the USB connector 30 is connected to the low-power USB port 12, the USB-corresponding device 10 supplies only the low power (100 mA/5 V) to each section of the bus power device 40. Therefore, the bus power device 40 is unusable.
FIG. 10 is a block diagram of a configuration of a conventional bus power device 50. In the drawing, like reference numerals as those in FIG. 9 designate like parts, and their explanation is omitted. When the USB connector 30 is connected to the low-power USB port 12, the bus power device 50 in the drawing receives high power from a separate power source and is driven.
The bus power device 50 additionally has a direct current (DC) jack 51 and a switcher 52. The DC jack 51 is a terminal that connects an alternating current/direct current (AC/DC) adaptor (not shown) as a separate power source. The DC jack 51 is connected to the bus power line 31 via the switcher 52.
The AC/DC adaptor converts an alternating current to a direct current, and generates a DC voltage/current. The switcher 52 has a function of switching the connection destination of the bus power line 31 to the USB connector 30 or the DC jack 51.
The operation by the bus power device 50 is explained with reference to a flowchart shown in FIG. 11. In the above configuration, when the AC/DC adaptor (not shown) is connected to the DC jack 51 in a state that the switcher 52 switches over to the DC jack 51, at step SB1 shown in FIG. 11, the AC/DC adaptor supplies the high power (500 mA/5 V) to each section via the DC jack 51, the switcher 52, and the bus power line 31, so that each section is activated.
Specifically, the voltage adjustor 24 supplies a voltage of 3.3 V to the USB/ATA converter 21, so that the USB/ATA converter starts operation. When the hard disk power source switch 44 is turned on under the control of the MPU 43, the bus power line 31 supplies power to the hard disk 23, so that the hard disk 23 is powered on.
When the USB connector 30 is connected to the low-power USB port 12 and is plugged in at step SB2, the USB-corresponding device 10 acknowledges the bus power device 50 at step SB3. At step SB4, the bus power device 50 starts the operation.
As described above, in the bus power device 40 shown in FIG. 9, the current detector 42 detects a current that flows through the bus power line 31. When the current exceeds a predetermined value, the secondary battery 41 assists the current according to the current assisting system.
In FIG. 9, when a connector contact resistance from the high-power USB port 11 to a unit to be driven (such as the hard disk 23) is large or when a cable is long, a large voltage drop occurs.
For example, assume that the high-power USB port 11 has a voltage of 5 V, and the operation guarantee voltage of the hard disk 23 is 4.75 to 5.25 V. In this case, when the voltage drops in excess of 0.25 V, a voltage supplied to the hard disk 23 becomes less than the operation guarantee voltage of 4.75 (5−0.25) V. As a result, the hard disk 23 does not operate.
However, according to the current assisting system in the bus power device 40, only the current that flows through the bus power line 31 is detected. Therefore, the inoperative state due to the voltage drop cannot be avoided.
According to the conventional bus power device 40, the load (the battery voltage) of the secondary battery 41 changes depending on the operation status (charging, access to the hard disk 23, or data transfer) of the bus power device 40. Despite this change, the bus power device 40 compares the battery voltage of the secondary battery 41 with one threshold value, and makes the battery remaining level display unit 47 display the battery remaining level based on a result of this comparison. Therefore, an accurate battery remaining level cannot be understood.
According to the conventional bus power device 40, the charger 45 charges a constant current to the secondary battery 41. Therefore, even when it is necessary to charge in a short time, a quick charging cannot be achieved.
When the conventional bus power device 50 shown in FIG. 10 is connected to the low-power USB port 12, a separate power source (the AC/DC adapter) is essential. Therefore, the bus power device 50 cannot be used without the separate power source.